Since January, when we installed an M620 Sandybridge cluster from Dell,
we have had issues with power and performance to compute nodes. Dell
apparently continues to look into the problem but the usual responses
have provided no solution. Firmware, BIOS, OS updates all are fruitless.
The problem is that the node/CPU is power capped. We first detected
this with the STREAM benchmark, a quick run, which shows memory
bandwidth around 2000 instead of the normal 13000 MB/s. When the CPU is
in the C0 state, this drops to around 600.
The effect appears randomly across the entire cluster with 5-10% of the
nodes demonstrating some slower performance. We don't know what
triggers this. Using "turbostat" we can see that the GHz of the cores
is >= 1 in most cases, dropping to about 0.2 in some of the worst cases.
Looking at the power consumption by either the chassis GUI or using
"impitool sdr list" we see that there is only about 80 watts being used.
We run the RH 6.x release and are up to date with kernel/OS patches.
All firmware is up to date. Chassis power is configured as
non-redundant. tuned is set for performance. Turbo mode is
on/hyperthreading is off/performance mode is set in BIOS.
A reboot does not change this problem. But a power cycle returns the
compute node to normal again. Again, we do not know what triggers this
event. We are not overheating the nodes. But while applications are
running, something triggers an event where this power capping takes effect.
At this point we remain clueless about what is causing this to happen.
We can detect the condition now and have been power cycling the nodes in
order to reset.
If anyone has a clue, or better yet, solved the issue, we'd love to hear
the solution!
Thanks,
Bill